This application claims priority under 35 U.S.C. 119 of German Patent Application Number 10156048.6 filed Nov. 15, 2001.
The invention relates to a reference voltage source including a bipolar transistor having a base, a collector and an emitter electrode.
One such reference voltage source is known from the German semiconductor circuitry textbook, xe2x80x9cHalbleiter-Schaltungstechnikxe2x80x9d by O. Tietze and Ch. Schenk, published by Springer-Verlag, 9th Edition, pages 558 et seq. In this known reference voltage source the base-emitter voltage of a bipolar transistor is used as the voltage reference. The temperature coefficient of this voltage of xe2x88x922 mV/Kelvin is remarkably high for a voltage value of 0.6 V. Compensating this temperature coefficient is achieved by adding a temperature coefficient of +2 mV/Kelvin generated by a second transistor. It can be shown that by operating the two transistors with different current densities a highly accurate reference voltage of 1.205 V can be achieved, exhibiting no dependency on temperature.
In this known reference voltage source each of the two transistors is in a separate branch of the circuit. The currents flowing in the two circuit branches are set so that the sum voltage has the desired temperature coefficient. The voltage follower stage is formed by an operational amplifier generating the reference voltage at its output. The output voltage of the operational amplifier is, in addition, fed back to the base terminals of the two transistors.
Since in reference voltage sources of the aforementioned kind two circuit branches are needed to generate the reference voltage, such reference voltage sources require a feedback/combination stage. This makes such circuits relatively complicated. They necessitate more components and have a higher current consumption. A further disadvantage is that a relatively high supply voltage is needed which needs to attain at least the band gap voltage of the semiconductor employed, this being at least 1.2 V for silicon as the material used as a rule.
The invention is thus based on the objective of providing a reference voltage source of the aforementioned kind in which for generating the reference voltage only a single circuit branch is needed and which, in addition, can be operated with smaller supply voltages than circuits hitherto in thus featuring a lower current consumption.
In accordance with the invention this objective is achieved by a reference voltage source of the aforementioned kind including a bipolar transistor which is characterized by it further comprising a Schottky diode whose anode is connected to the base electrode of the bipolar transistor and whose cathode is connected to the collector electrode of the bipolar transistor, the currents flowing through the Schottky diode and the collector-emitter circuit of the bipolar transistor each being set so that a temperature-independent reference voltage (VREF) materializes at the collector electrode of the bipolar transistor.
The reference voltage source in accordance with the invention has the advantage of requiring fewer components whilst having a lower current consumption.